▎ 摘　　要

A boron-doped graphene quantum dot (B-GQD) as a metal-free multimodal contrast agent (CA) for safe magnetic resonance imaging and fluorescence imaging is reported. In vivo T1-weighted magnetic resonance images show that B-GQDs induce significant contrast enhancement on the heart, liver, spleen, and kidney, and sustain for more than 1 h, about 10 times longer than Gd-based CAs currently used in clinic.